Update System.Drawing unsupported warning for .Net Core

[svick]

The remarks for the System.Drawing namespace say:

Caution
Classes within the System.Drawing namespace are not supported for use within a Windows or ASP.NET service. Attempting to use these classes from within one of these application types may produce unexpected problems, such as diminished service performance and run-time exceptions. For a supported alternative, see Windows Imaging Components.

This warning seems to be specific to .Net Framework and Windows, so it leaves the question of support of System.Drawing on .Net Core and on Unix open.

I think this warning should be updated, to make it clear what the support status of System.Drawing on .Net Core is.

[mairaw]

Thanks @svick for your feedback. @safern, @maryamariyan can you comment on this?

[safern]

System.Drawing should be supported in .NET Core on both Windows and Unix, however the constraint is as follows:

• Unix: libgdiplus should be installed in the running OS (the recommended minimum version is 6.0.1)
• Windows: GDI+ should be available in the running SKU... for example, nano and iot, don't provide GDI+ APIs.